package com.carl.math;

import java.util.Scanner;

public class question_07 {

    public static void main(String[] args) {

        // 两点间距离

        Scanner sc = new Scanner(System.in);
        double x1 = sc.nextDouble(),y1 = sc.nextDouble();
        double x2 = sc.nextDouble(),y2 = sc.nextDouble();

        double dx = x1 - x2,dy = y1- y2;


        double dist = Math.sqrt(dx * dx  + dy * dy);

        System.out.printf("%.4f",dist);
    }
}
